What is the reason for homosexuality in humans?

Now, first off, I am not a homophobe, or a Bible-thumper. In fact, I have several gay friends.

I'm trying to find if there is a biological basis for human homosexuality. Animal homosexuality has been proven to occur when members of the opposite sex are unavailable during the short mating seasons, so animals satisfy themselves with simulated mating at least. Although we still don't know if animals are also capable of non-mating "emotional" bonding.

In humans, several theories have been proposed. One says there is difference in brain structure, but that has not been proven I think. Second one says it is a result of social upbringing, dysfunctional families, etc. Third one says it is capable of being passed down through the genes. Fourth one says it's nature's way of eliminating weak individuals.

Humans don't need the urging of a mating season to have sex, so the unavailability of members of the opposite sex cannot be a reason. It does not serve a reproductive purpose. Emotional bonds are often formed by individuals of the same gender, but it does not lead to sexual relationships.

So, why?

Please be as open and candid as you feel comfortable. This is an open discussion.

Jul 19 2011:
During my courses of animal psychology, the professor came with the following hypothesis:
If man were all competing for women, there would be a lot of blood and fighting going on.
We have a set of genes that makes us friendly towards men.
If one has much of those "friendly" genes, the likelihood of him being gay is quite high...
There are environment factors who influence this threshold...

The strength of this idea is that it also explains why gay people are not selected out of the population (as the friendly genes have advantages)

Jul 20 2011:
I'd just like to second this. It appears the consensus in psychology at the moment is that homosexuality has the advantage of reducing morbidity and mortality from aggression and defense, increasing the chances of procreation by the simple fact that the organism isn't dead or injured. This fits with evolution, so the two ideas are compatible.

That does make a lot of sense. I never looked at it that way, good comment.

Just a quick question off topic, you said you where doing animal psychology.
I read somewhere that animals do not have human emotions, they may get angry and attack, but it will be short lived and soon forgotten, and they wont hold a grudge like humans do. It all so said that animals living in close proximity with people may be affected to some degree with the human emotions. One debate was that pets seem to love their owners and can get depressed.

It would be great if you could shed some light on this topic and tell me what you can.

Jul 20 2011:
Depends on what you mean by 'human emotions'.
And also on what animals.

Insects have reflex-emotions: for example if you make a threatening movement towards a mantis, it lifts its forelegs to defend/attack. If you gently put them down, the mantis forgets it is 'angry'.

As you move towards vertebrates, our brain structure is already comparable, and will have emotions that do trigger responses...
I do think they can learn as well. Look at the talk about Crows :http://www.ted.com/talks/lang/eng/joshua_klein_on_the_intelligence_of_crows.html
they sure can remember those who angered them in the past.
Same goes for elephants and dogs.

Depression among pigs is also known and documented. Social animals who don't have companions (i.e. alone) tend to behave as if depressed. (Dogs, Pigs, African Grey parrots, baboons...)

As of how they feel, we do need to be careful not to anthropomorphisize, but we cannot "know" how other people feel exactly either (solipsistic problem), though we assume it is comparable.

So I would claim that emotions, as they reside in very basic neural structures, do appear in animals, and depending on the species (especially birds and mammals), it gets quite complex and more human-like.

As our emotions are also influenced by our culture and frontal cortex, there probably are differences in nuance and workings of our emotions, but there is much overlap.

However, if according to this theory, the purpose of those genes was to be male-friendly, even then the ultimate motive of that male-friendliness is to eliminate competition for female-mating. We don't see that. Gay males want to mate with males.

Regardless of how "concentrated" the "gay gene" becomes, it should only result in male-friendliness and female-mating.

Comment deleted

Jul 20 2011:
Yes, altruism can be explained on a societal evolutionary basis. The remembrance of self-sacrifice and repay of it in the future time of need is very real and understandable.

"Evolution is not goal oriented"

I don't entirely agree. Evolution is a process of outputting a set of randomized solutions to a necessity. One or more of them might work. However, the others still remain in marginal amounts due to the recessive nature of genes. So basically, evolution is capable of wonderful trial-and-error processes, but is incapable of entirely getting rid of the "errors". How about that?

Jul 20 2011:
Why is it that we like to find "a reason" for everything?

If we are simply biological beings, it is hard to come up with a "reason" for homosexuality.

If we are social beings, then we might be able to think of some reasons: the roles some homosexuals play in the community are often unique and very constructive. For example, my pseudo-brother, Pat, and his partner are extremely supportive of my mother and have been for the last 30 years or so (that's how Pat became my pseudo-brother.) Their behaviour is not limited to my mother either, they are very involved in supporting "senior citizens." Through Pat and his friends, I have found that this group of men play a very active and socially cohesive role.

Maybe groups that contain some gay folks have a survival advantage.

Not very scientific, I know, but there you have it.

Maybe there is no reason. Maybe there are just gay people and that's all there is to it.

Aug 9 2011:
I recently read a brief synopsis of a genetic theory for why there are male homosexuals. ( I suppose there could be a parallel theory for female homosexuals.) The male homosexual theory goes somewhat like this:

Women choose their male sexual partners according to the behaviors exhibited by the males that are available to them. Some women prefer men who are communicative, caring, emotive, and reassuring. These are stereotypical female traits. Other women prefer men who are assertive, competitive, uncommunicative, and powerful; typical male traits. Assuming that these traits are due to several different genes, then men will exhibit these traits in different degrees according to the particular alleles (alternative forms of the same gene) that they have inherited from their parents. If you inherit enough of the "female trait" alleles, then you will appeal to the female-trait-preferring women, and you will pass along some of your female-trait alleles to your children. But if you inherit too many of the female-trait alleles, you will be a male homosexual and you may not have children.

It's rather like the genetic explanation for the persistence of sickle-cell anemia among certain populations in Africa. Sickle-cell anemia is inherited, and can be deadly, so why aren't these genes eliminated via natural selection? Well it turns out that a certain combination of alleles results in sickle-cell anemia, but a different combination of alleles of these same genes confers resistance to malaria. The malaria-resistance selects for these alleles, and the sickle-cell anemia selects against these alleles, leading to a steady-state balance.

Similarly, the female trait alleles reach a steady state among human males, resulting in a certain percentage of male homosexuals. Or so the theory goes ....

Aug 9 2011:
I have seen cases of people turning into homosexuality in 'joint-families'- cases of 10-15 adoloscents sharing a single room, sexually fiddling with each other as a part of 'growing-up' and some of these turning into homosexuals (basically the 'bottom' men at the 'receiving' end). So environment for sure plays a role.

Then there are some people who are just 'born with it', some curious & discreet and some open about it.

As I interpret it, mentally we all (men & women) tread somewhere between the two extreme ends of masculinity and feminity. All of us are different possible variants (with all permutation & combinations of physical body & sexual behaviour) of humans conditioned by our concept of normal/abnormal/right/wrong, thereby exhibiting the image we want to project or stick to.

And I do also feel that at some level (conscious or sub-conscious), sexuality, as everything else, is a choice!